Glass, transparent films and so forth on which shielding films have been formed by coating, sputtering or the like method are conventionally used for the purpose of shielding the sunlight that enters through window materials of constructions, window materials of automobiles, and so forth.
These shielding films are roughly grouped into a heat ray reflection type and a heat ray absorption type.
More specifically, many of the heat ray reflection type are metallic thin films of Al, gold or the like formed on transparent substrates such as glass and transparent films by sputtering, ion plating, vacuum deposition or the like method, as disclosed in, e.g., Japanese Patent Application Laid-open No. S57-59749. Such metallic thin films reflect light having wavelengths ranging from the visible region up to the infrared region, and hence can make the substrate less rise in temperature and have very good heat insulating properties. Since, however, they also reflect light having wavelengths in the visible region, they have had a disadvantage that they are so glaring as to look like mirrors and are unfavorable in view of design quality.
On the other hand, in the heat ray absorption type, substrates are coated with, or kneaded therein with, such organic dyes or organic pigments as those disclosed in Japanese Patent Application Laid-open No. 2000-80319, to color the substrates so as to shield the heat rays. Shielding films of this type are widely prevailing especially because the dyes are inexpensive and are easy to handle, but are disadvantageous in that they have poor weatherability. Also, shielding films of this type can be free of any glaringness due to the reflection in the visible region and have superior design quality, but have had a disadvantage that they have lower heat insulating efficiency than those of the heat ray reflection type because the former inevitably allows the heat energy absorbed in the substrates, to radiate into the interior. Still also, shielding films making use of the above organic dyes or organic pigments, or coloring materials such as oxides, sulfides or sulfates of metals, have had no properties that may achieve both high shielding properties and restraint of glaringness. Furthermore, they have had a problem that, because of use of coloring materials, they have so excessively bright color tone in many cases as to come into depthless or reposeless appearance.
The present invention has been made taking note of such problems. Accordingly, a subject of the present invention is to provide a visible light absorbing film which enables restraint of glaringness in the visible region in the heat ray reflection type one and also enables substrates to maintain even their heat insulating properties, and to provide a structural member having this visible light absorbing film, and a visible light absorbing ink which forms the visible light absorbing film.
Then, the present inventors have made extensive studies in order to settle the above subject. As the result, they have come up with a discovery that, where a visible light absorbing film is formed on at least one side of a substrate having solar radiation reflecting properties, using a visible light absorbing ink containing fine particles which may selectively absorb the visible-region light and transmit the near-infrared-region light and infrared-region light, only the visible-region light can selectively be absorbed as the substrate is kept to have its solar radiation reflecting properties, in virtue of the action of the visible light absorbing film formed. The present invention has been accomplished on the basis of such a technical finding.